PROJECT SUMMARY/ABSTRACT: Retinitis pigmentosa (RP) due to mutations in the rhodopsin gene is one of the leading causes of inherited blindness. More than 150 mutations in the rhodopsin gene have been associated with RP and most of these mutations cause autosomal dominant RP (adRP), although some cause autosomal recessive RP (arRP). Current treatments are not effective and the quality of life of the patients is severely affected by loss of visual acuity or the total loss of vision. Although some major advances in the treatment of RP have been made using viral gene therapy for gene supplementation, this approach can be limited by cell tropism, size of the expression cassette to be transferred, and host immunity to repeat infections. Recently, we and others have used unique self-compacted DNA nanoparticles (NPs) to transport the vector into the cell nucleus, where it is efficiently expressed within 1 hour. Our own proof-of-principle studies have demonstrated that these NPs are safe, effective and non-toxic after subretinal delivery to the eye. Most importantly, NPs are capable of delivering large genes to the retina. Recent studies have shown that this particular NP system may be clinically viable and may be able to provide a vehicle for delivery of therapeutic genes for the treatment and prevention of many different retinal diseases. Current strategies use cDNA for gene targeting, but genomic DNA (gDNA), which better preserves the stability of the message and endogenous gene regulation, may be a more effective method to elicit therapeutic rescue after gene supplementation. Here we will test this hypothesis by taking advantage of our large-capacity, highly efficient NPs to deliver cDNA or gDNA for rhodopsin to two well-characterized RP mouse models. In Aim 1 we will test the ability of NPs carrying either the cDNA or gDNA of the rhodopsin gene to rescue the arRP Rho-/- (RKO) model. In Aim 2, having optimized a pure gene supplementation strategy, we will combine this approach with allele independent knockdown for the treatment of the gain-of-function P23H Rho+/- model of adRP. We will modify the delivery vector to house a specifically-designed short hairpin RNA (shRNA) of RNA interference (RNAi) to knockdown both the wild-type (WT) and mutant rhodopsin alleles, and concurrently deliver a knockdown-resistant WT rhodopsin (as either a cDNA or gDNA based on results from Aim 1). These strategies should achieve improved, therapeutically-effective levels of expression and rescue in dominant P23H Rho+/- mice. Our goal is to attain full functional and structural rescue in the RKO and the P23H Rho+/- models by using NP-mediated expression of cDNA and/or gDNA in concert with RNAi. Thus, the potential scientific and clinical benefits of these proof-of-principles experiments are substantial. Payoffs will be evident at both the theoretical and applied levels: at the theoretical level, we are working toward a better understanding of the applicability of bio- science models to human populations. On the applied level, our results will directly affect quality of life and could be of potential benefit for treating arRP and adRP by providing new technology options.